Volume 49, Issue 2

Seagrass distribution and sediment biogeochemical conditions were measured around Libong Island in the Andaman Sea, Thailand. Seagrass diversity was moderate for a tropical site (four species found: Cymodocea rotundata , Enhalus acoroides , Halophila ovalis and Thalassia hemprichii ), with the diminutive species H. ovalis particularly abundant and perhaps serving as important food for dugongs present in the area. Although the sediment organic matter content was low in the seagrass meadows, the sulfate reduction rates were high (48–138 mmol m -2  d -1 ). A significant positive relationship between belowground biomass and sulfate reduction rates across the seagrass species examined indicates that stimulation of microbial activity in the rhizosphere sediments is controlled by the biomass of roots and rhizomes, rather than by specific seagrass characteristics (e.g., morphology, plant activity). The low iron contents in the seagrass tissues were within the range suggested for nutrient limitation. Sediment sulfur pools, in particular pyrite pools, were high and most of the available iron was bound in sulfides, which may cause iron limitation in seagrass tissues. High sediment sulfide production and sulfide accumulation in concert exert sulfide stress on the seagrasses, as indicated by an accumulation of elemental sulfur in the plants examined, suggesting that tropical seagrasses are prone to sulfide intrusion, similar to findings for temperate seagrasses.

The dynamics of Ruppia cirrhosa were studied over two years in two coastal lagoons on the Corsican coast (France, Mediterranean Sea). The lagoons differed in type of eutrophication: (1) Biguglia lagoon (urban and industrial effluent, agriculture, runoff from catchment area) and (2) Santa Giulia lagoon (tourist pressure in summer). Spatio-temporal variability of R. cirrhosa occurrence was monitored on permanent transects. We also monitored temporal changes in density, aboveground/belowground biomass and organic matter. Most of the parameters studied along the transects show variations with season and site. Density and aboveground biomass of R. cirrhosa in Biguglia lagoon were lower when Ulva species were present. This may be related to differences in nutrient availability. During the first year of the study, rainfall was greater with concomitantly higher nutrient inputs, which may account for the higher values of measured parameters in the first year. The results suggest that environmental parameter variations affect the functioning of R. cirrhosa meadows.

Identification of Halophila ovalis samples from various parts of the world has long been accompanied by taxonomic uncertainties because of morphological variability. This led to the hypothesis that H. ovalis represents a “collective species” which may include cryptic species. Recent studies applying molecular techniques to the assessment of phylogenetic relationships in the genus Halophila also came to a similar conclusion. In this study, one Halophila species from Japan, previously described as H. euphlebia and later treated as a synonym of H. ovalis , was critically re-examined using molecular phylogenetic analyses of the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA. Morphological examinations of vegetative and reproductive structures were also undertaken. Results obtained from both morphological and molecular data, combined with a critical review of the relevant literature provide support for recognition of the plant in question as being distinct from H. ovalis . The entity conforms to Makino's description of H. euphlebia . This raises the current number of Halophila species in Japan to three: H. ovalis , H. decipiens and H. euphlebia .

A new species of Ganonema, G. vermiculare , is described based on specimens collected from 11–17 m depths in southwestern Puerto Rico. When living, algae appear chalky white with a maroon margin. The new species is not distinguished by any autapomorphies, but is distinct from its 13 congeners by a combination of characters, foremost of which are the ovoid cells of the assimilatory filaments and the hollow cylinder of calcification located at the outer medulla. Assimilatory filaments extend to 300 μm beyond the ring of calcification. Cells of the cortical fascicles cut off abundant rhizoidal filaments, which grow back into the medulla, where they intersperse with and lie parallel to the longitudinally oriented medullary filaments. Carpogonial branches are mostly four cells in length, originate on proximal cells of the cortical fascicles, and become conspicuously surrounded by sterile filaments following fertilization. Carposporophytes are compact, measuring from 150 to 220 μm in diameter.

Antithamnionella multiglandulosa is described as a new species from the Atlantic side of the Iberian Peninsula. Distinguishing features of the new species are: the 3–6 simple whorl-branches produced per axial cell, the presence of series of up to 4 gland cells on whorl-branches, and whorl-branches with periaxial cells similar in size to contiguous branch cells. We present a comparative study of European or other similar Antithamnionella species, including A. ternifolia , A. elegans , A. spirographidis , A. boergesenii , A. multiramosa , A. verticillata , A. tormentosa and A. australis . There are now five species of Antithamnionella in northern Spain and Portugal, and six along the European Atlantic coasts.

A study of the benthic algal macroflora of Linosa Island (Straits of Sicily, Mediterranean Sea) is presented, aiming to verify possible floristic changes that have occurred in the area, last studied in 1973. We found noticeable changes in the benthic flora, which is now poorer in species than that recorded in the literature (233 species against 305), with a minor decrease in Phaeophyceae and Chlorophyta, and a more significant decrease in the number of Rhodophyta. Only 178 species in the present flora were reported previously, while 127 previously reported were not found during the present study. Conversely, 55 species were newly found. Several species of Fucales, like Cystoseira brachycarpa , C. sauvageauana , C. spinosa , C. zosteroides , Sargassum acinarium and S. trichocarpum , which are characteristic of the Mediterranean Sea photophilic communities on hard substrata and sensitive to any environmental changes, have disappeared.

Seasonal and spatial patterns in the occurrence of Noctiluca scintillans , a dinoflagellate responsible for most of the red tides in the coastal waters of Hong Kong, were studied in Tolo Harbour and Mirs Bay from July 2003 to June 2005. N. scintillans density and chlorophyll a concentration were highest in the inner part of the semi-enclosed Tolo Harbour and decreased towards Mirs Bay, which is exposed to currents from the ocean. N. scintillans became abundant during winter and early spring, but densities recorded between December 2004 and April 2005 were much higher than those recorded between December 2003 and March 2004. The density of N. scintillans did not correlate with chlorophyll a concentration, but cell size tended to decrease as chlorophyll a concentration increased. Cells collected from Tolo Harbour were more likely to contain food than those collected from Mirs Bay. Dense populations of N. scintillans usually appeared first in Mirs Bay, but peak densities were always much higher in Tolo Harbour than in Mirs Bay. These observations suggest that N. scintillans was prevented from reaching high abundance in Mirs Bay by insufficient food and strong water currents. Conversely, nutritional and hydrographical conditions inside Tolo Harbour allow N. scintillans populations to reach high densities.

Original material of Melosira arctica was examined. Species circumscription is emended to include detailed frustule fine structure and, for the first time, the basic morphometrics of the population from original material have been established using light and electron microscopy. This original population, collected in 1850, was compared to three contemporary populations of this taxon, collected at Arctic Ocean stations ranging from latitude of 71° to 76° N and from longitude 77° to 173° W. As a result of morphometric examination, a new variety, M. arctica var. krembsii , is proposed. The new variety differs from the nominate variety by finer perforation of the valvocopulae, by fewer marginal rimoportulae in 10 μm located further above the mantle margin, by fewer rimoportulae on the valve face, and by finer striation of the valves. Based on published illustrations, we suggest that M. arctica var. krembsii may be more common at latitudes south of 70° N, while the nominate variety occurs in more polar seas.

In this study, we investigated changes with culture age in growth rate, ΦPSII e-max (the maximal effective quantum yield of PSII,=F v /F m ), the photosynthetic parameters α, rETR max and I k , fatty acid composition and macromolecular content (via IR spectroscopy) in batch cultures of Phaeodactylum tricornutum and Chaetoceros muelleri . ΦPSII e-max , and the initial slope of the photosynthesis vs. light curve (α) in the two diatoms exhibited almost the same pattern of variation over the experimental period, first increasing slightly to a maximum value, then decreasing with increasing culture age. There was also a significant decrease, with increasing culture age, in the parameters rETR max and I k in both diatoms. FT-IR spectra of P. tricornutum and C. muelleri all showed changes over the growth period. The bands attributed to lipids (C-H stretching between 3000 cm -1 and 2800 cm -1 along with the ester C=O 1740 cm -1 ) in both diatoms showed the same tendency, increasing with increasing culture age over the entire growth period, consistent with the onset of major nutrient (P) limitation. Changes with culture age were also found in the fatty acid composition. P. tricornutum showed a marked increase in the levels of 16:1 n-7 and 18:1 n-9 and a marked decrease in the levels of 16:3 n-4 and 20:5 n-3 with increasing culture age. There was a slight variation in the fatty acid composition of C. muelleri related to culture age, with the largest increase shown by 16:0 and the largest decrease by 16:3 n-4.

D-Fructose-1,6-bisphosphate aldolase (0.042 mg) was purified from a red alga, Gracilaria chorda , by ammonium sulfate precipitation, followed by ion exchange and hydrophobic interaction chromatographies. The enzyme was purified 87-fold resulting in a final specific activity of 10.7 units/mg and a homogeneous appearance on electrophoresis. By SDS-PAGE analysis of the enzyme, two protein bands corresponding to molecular masses of 45 kDa and 39 kDa were observed. The enzymic activity disappeared in the presence of 0.5 mM EDTA, but was restored to 109% of the original untreated activity by the addition of 1 mM ZnSO 4 subsequent to EDTA treatment. The enzyme was activated up to 5.5 times the original untreated activity by the addition of 500 mM KCl, and had a narrow optimum pH around 7.2. On the basis of these results, the G. chorda D-fructose-1,6-bisphosphate aldolase was characterized as a class II aldolase.

Growth and docosahexaenoic acid (DHA) formation in Schizochytrium mangrovei Sk-02 were studied in yeast extract-glucose (YEG) media supplemented with either artificial sea salts (ASS) or a simplified salts medium consisting of magnesium sulfate and/or sodium chloride. With increasing concentrations of ASS, biomass increased from 9 (no ASS) to a maximum of 21 g l -1 (at 2.1 M ASS or 68 g l -1 ). Addition of manganese increased these values to 17 (no ASS) and a plateau of 24 g l -1 (at >0.25 M ASS). Replacing ASS with magnesium sulfate and/or sodium chloride and manganese as an additional factor suggested that maximal biomass (24 gl -1 ) could only be achieved when both magnesium sulfate and manganese were added. As significant carry-over of elements in the inoculum was observed, the latter was washed in further experiments. Addition of an optimal concentration of ca. 5 mM magnesium sulfate to YEG-media then resulted in a maximum biomass level of ca. 24 g l -1 and 5.2 g l -1 DHA in 72 h. Additional supplementation with sodium chloride (8 mM) significantly stimulated biomass formation when magnesium sulfate addition was below 0.8 mM, but not at higher levels of the latter. However, cultivation time was reduced by ca. 24 h, resulting in formation of ca. 5.5 g l -1 DHA in only 48 h. By replacing ASS with magnesium sulfate plus sodium chloride, the sum of the concentration of these four elements in media could be reduced ca. nine-fold, while achieving similar biomass- and DHA-yields. The concentration of chloride, a compound highly corrosive to steel fermenters, was reduced more than ten-fold.